<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        body{
            position: relative;
        }
        .box{
            width: 100px;
            height: 100px;
            background: skyblue;
            position: absolute;

        }
    </style>
</head>
<body>
        <input type="button" value="开始" id="btn">
        <div class="box"></div>
        <script>
            function $(ele){
                return document.querySelector(ele);
            }
            let speed=1;
            $('#btn').onclick=function(){
                let time=setInterval(function(){
                if($('.box').offsetLeft>500){
                    clearInterval(time);
                }else{
                    $('.box').style.left=$('.box').offsetLeft+speed+'px';
                }
            },20);
            }
           
        </script>
</body>
</html>